It is well known that the optimal hydrophilic contact lens should have as high water content as possible, yet have good mechanical integrity and notch strength. High water content lessens the irritation of the eye, establishes a high degree of hydrophilicity which leads to better lubrication during blinking, and most importantly, it is known that the permeability of oxygen through the lens increases exponentially with water content. Furthermore, the lens should have a large effective pore size so as to allow the passage of not only low-molecular weight tear film components, such as metabolites (glucose, urea, lactic acid, etc.) and ions, but also higher-MW components such as proteins and mucins, thus minimizing the effect of the lens on the distribution of these components in the preocular tear film (POTF) without the need for tear exchange under the lens. In prior art contact lenses these have represented conflicting requirements and compromises have had to be made. For example, good integrity requires a high degree of cross-linking and thus low water content and small effective porsize. Lenses such as Sauflon 70, which are made from copolymers of hydrophilic and relatively hydrophobic monomers, have a high water content, but the tear film over these lenses has been found to be definitely thinner and less stable than the normal POTF (note that some authors use the term pre-corneal tear film, or PCTF, instead of POTF), whereas the pre-lens tear film (PLTF) over lenses made from PHEMA, a very hydrophilic polymer, were found to be very similar to the normal POTF. Furthermore, the use of PVP (polyvinylpyrrolidone) to achieve high water content results in lenses which yellow with age.
The desired properties have been obtained, and the difficulties of prior materials have been overcome in a novel and unobvious manner by the present invention. Other properties and advantages will become apparent in what follows.